A potential source of energy that has not been well utilized to date is harvesting of waste kinetic energy. An example of a good use of otherwise wasted energy is regenerative braking systems used in hybrid cars. Regenerative brakes transform the kinetic energy of the car into electricity that is stored in the battery.
Another potential type of waste energy is the kinetic energy of moving or pressurized fluids, in either a man-made or natural system.
Many attempts have been made to harvest electricity from the deformation of various flexible or stretchy membranes in contact with a moving or pressurized fluid, such as auto tires, a rubbery tube that is stretched by ocean waves, or leaf-like ribbons that undulate in a river. Piezoelectric material is in some manner attached to the flexible membrane to convert the bending or stretching motions directly into electricity.
For example, Adamson et al. in U.S. Pat. No. 7,429,801, issued Sep. 30, 2008, teach the use of commercially available piezoelectric fiber composite material in some detail.
Other attempts to generate electricity from the kinetic energy of moving water first convert the complex motions of the water into a simpler type of motion, such as that of a waterwheel, a piston, or an oscillating (but not stretchable) membrane. Then the rotary or linear motion is converted into electrical energy.
Auto tires produce only tiny amounts of electricity, such as enough to transmit data from an internal air pressure sensor. This is a useful, but very limited application. Other systems in the patent literature for generating larger amounts of electricity with stretchy membranes require dedicated, rugged apparatus fabricated from special materials. This also limits their usefulness because of the high costs of fabrication, permitting, and installation.
At least one pilot scale turbine has been placed in a municipal water main. This appears useful in certain cases where the water has far more energy than it needs to arrive at its ultimate destination, such as when water has been pumped over mountains then flows down by gravity. In the more typical case of water pressurized by a pump for the purpose of causing it to flow in a relatively level pipe, any apparatus that impedes the flow is probably not beneficial.
There is still a need for systems to harvest waste kinetic energy, such that from moving water, that do not impede the flow of the water. In the case of pumped water or other fluid, it is especially vital that energy is not actually “stolen” from the pump. There is further a need for energy harvesting systems that use conventional materials and construction techniques.